The present invention relates to a non-radiative dielectric line and an integrated circuit thereof suitable for a transmission line or a circuit used in a millimetric wave frequency band or a microwave frequency band.
Hitherto, a dielectric line in which, as shown in FIG. 26, a dielectric strip 3 is disposed between two conductive plates 1 and 2 approximately parallel with each other has been used as a dielectric line in a millimetric wave frequency band or a microwave frequency band. In particular has been developed a non-radiative dielectric line (referred to an NRD guide below) in which the propagation area is arranged within only a dielectric strip portion by reducing the spacing between the conductive plates to have no more than a half-wave length of the propagation wavelength of an electromagnetic wave.
When such the NRD guide is formed, PTFE is mainly used for the dielectric strip while hard aluminum is mainly used for the conductive plate. However, since the coefficients of linear expansion of these materials are largely different, a problem that the dielectric strip slips relatively from the conductive plate during the cycle of temperatures has risen. Therefore, a structure for fixing the dielectric strip slip to the conductive plate is important in the point of weather resistance.
In forming a millimetric wave circuit module by combining several components using NDR guides, when the NDR guides are connected to each other between the components, positioning of each of the NDR guides for connecting to each other is required.
Therefore, as shown in FIG. 27, a conventional fixing structure of the dielectric strip, in which a protruding portion is formed at a predetermined position of the dielectric strip while an associated hollow portion is formed in the conductive plate such that both portions are mated with each other, is disclosed in Japanese Unexamined Patent Publication No. 08-8617.
On the other hand, NRD guide, in which slots are formed on respective surfaces, opposing each other, of the conductive plates and a dielectric strip is disposed between the slots, such that only a single mode of an LSM01 mode can be transmitted, is disclosed in Japanese Unexamined Patent Publication No. 09-102706.
In the NRD guide having the structure shown in FIG. 27, it is advantageous that the dielectric strip be directly disposed between the conductive plates by a method such as injection molding; however when the dielectric strip is manufactured by a method such as cutting, the processing is difficult to perform. The larger the protruding portion of the dielectric strip 3 in size, the more securely it is mated with the conductive plate; however when it is too large, the electromagnetic field distribution is disturbed, generating reflections, so that characteristics as a transmission line may result in problems.
In the above-mentioned NRD guide having the conductive plates with slots formed thereon, the dielectric strip is positioned by mating with the slots of the conductive plates in the direction orthogonal to the propagating direction of the electromagnetic wave. However, the dielectric strip cannot be fixed in the propagating direction of the electromagnetic wave, which may result in the dielectric strip slipping in the propagating direction of the electromagnetic wave due to variations in ambient temperature, etc.
Accordingly, it is an object of the present invention to provide a non-radiative dielectric line and an integrated circuit using the same by solving the above-mentioned problems.
A non-radiative dielectric line according to the present invention comprises: two conductive plates approximately parallel to each other, slots opposing each other being respectively formed on the two conductive plates; and a dielectric strip disposed between both the slots, wherein convex portions protruding in the lateral direction to the propagating direction of an electromagnetic wave or concave portions recessed in the lateral direction to the propagating direction of an electromagnetic wave are formed at a predetermined position of the dielectric strip while concave portions or convex portions mating with the convex portions or the concave portions, respectively, of the dielectric strip are formed on internal surfaces of the slots in the two conductive plates.
Owing to this structure, the dielectric strip is fixed in the propagating direction of the electromagnetic wave by mating of the convex portions or the concave portions of the dielectric strip with internal surfaces of the slots of the conductive plates, while being fixed in the direction orthogonal to the propagating direction of the electromagnetic wave by mating with the slots of the conductive plates.
In another aspect of a non-radiative dielectric line, corner portions of the concave portions or the convex portions in the dielectric strip or in the slots of the two conductive plates may have a curved surface shape. For example, in forming corner portions of the concave portions or the convex portions in the dielectric strip or in the slots of the conductive plates to have a curved surface shape equivalent to part of a cylindrical surface, when the dielectric strip is cut from a PTFE plate with an end mill, the dielectric strip having the concave portions or the convex portions with corner portions having a cylindrical surface corresponding to the radius of the end mill can be easily formed. Likewise, when the slot of the conductive plate is formed with the end mill, the concave portion or convex portion with corner portions having a cylindrical surface corresponding to the radius of the end mill can be easily formed on the internal surface of the slot of the conductive plate.
In a further aspect of a non-radiative dielectric line, the dielectric strip is divided into two strips along a surface parallel to the propagating direction of the electromagnetic wave, wherein a gap between end faces of the two divided dielectric strips has a length which is an odd-number multiple of approximately one quarter of the guide wavelength of the electromagnetic wave propagating through the dielectric strip while the two divided dielectric strips are respectively mated with the two conductive plates by the convex portions or the concave portions.
Owing to this structure, in the connecting portion of non-radiative dielectric lines, reflected waves in each connecting surface between the dielectric strips cancel each other by being superimposed out of phase with each other, such that the effect of the reflection is reduced. Even when the two divided dielectric-strips move relative to the conductive plates due to variations in temperature, since the length of each gap produced therein is the same, the effect of the reflection is reduced regardless of variations in ambient temperature.
An integrated circuit of non-radiative dielectric lines according to yet another aspect of the invention comprises a plurality of the above-mentioned non-radiative dielectric lines, wherein the plurality of non-radiative dielectric lines are connected to each other. Owing to this structure, since the positional relationship between the plurality of non-radiative dielectric lines can be maintained to be stable, an integral circuit having small variations in characteristics due to variations in assembly accuracy and to variations in ambient temperature after assembling can be obtained.